1. Field of the Invention
The present invention relates generally to the field of surgical tissue removal, and more specifically to ultrasonic power delivery during surgical tissue removal procedures such as phacoemulsification.
2. Description of the Related Art
Phacoemulsification surgery has been successfully employed in the treatment of certain ocular problems, such as cataracts. Phacoemulsification surgery utilizes a small corneal incision to insert the tip of at least one phacoemulsification handheld surgical implement, or handpiece. The handpiece includes a needle that is ultrasonically driven once placed within an incision to emulsify the eye lens, or break the cataract into small pieces. The broken cataract pieces may subsequently be removed using the same handpiece or another handpiece in a controlled manner. The surgeon may then insert lens implants in the eye through the incision. The incision is allowed to heal, and the results for the patient are typically significantly improved eyesight.
As may be appreciated, the flow of fluid to and from a patient through a fluid infusion or extraction system and power control of the phacoemulsification handpiece is critical to the procedure performed. Different medically recognized techniques have been utilized for the lens removal portion of the surgery. Among these, one popular technique is a simultaneous combination of phacoemulsification, irrigation and aspiration using a single handpiece. This method includes making the incision, inserting the handheld surgical implement to emulsify the cataract or eye lens. Simultaneously with this emulsification, the handpiece provides a fluid for irrigation of the emulsified lens and a vacuum for aspiration of the emulsified lens and inserted fluids.
Pulse delivery has developed from a simple on/off arrangement through what is known as a burst delivery or pulse delivery, using fixed off periods or fixed duty cycles, to a specific pulse delivery such as the Whitestar pulse delivery method of Advanced Medical Optics Corporation of Santa Ana, Calif. Such designs provide the surgeon with different functionality useful in different phacoemulsification procedures, such as breaking the lens or removing the lens.
Previous systems have employed either an optimum phase angle to affect constant energy transfer into the tissue or apply a modulated voltage amplitude shaping pulse to control the phacoemulsification handpiece. These procedures can produce a significant amount of heat in the affected area. Care must be taken to avoid overheating of eye tissue during phacoemulsification while still performing the desired cutting or removal procedures. The risk of damaging the affected area via application of heat can be a considerable negative side effect.
Conditions may arise during ocular surgeries that reduce the cutting effectiveness of current pulse shaping designs. In particular, one undesirable effect exhibited by these systems is that small particles at the phaco tip can be knocked off from the tip at an undesirable time. The phaco tip must be sufficiently occluded by, or in contact with, the particle in order to effectively remove such particles. In order to circumvent or manage this effect, surgeons typically reduce the voltage amplitude shaping pulse to keep small particles from being knocked off at the tip. This method of reducing the voltage amplitude can materially limit cutting effectiveness. In general, blockage of the phaco tip dramatically reduces cutting effectiveness, as does any overall reduction in voltage amplitude applied.
Typical available systems may employ what is known as an occluded mode, wherein an occlusion or blockage of the phaco tip, such as by a piece of lens, is addressed in some manner. The typical way of addressing occlusion has been to cease operation until the tip is no longer occluded, i.e. simply releasing the pressure applied to the tip. This enables the operator/surgeon to manually move the tip and allow the occlusion to disengage from the instrument. Such an implementation simply monitors the pressure of vacuum on the tip, and when it exceeds a certain amount, the vacuum is released or no longer applied.
Increased efficiency in this environment is desirable, such that any devices or procedures that can lessen heat applied to the affected area or simplify the work of the operator surgeon is beneficial. Patient recovery time can be enhanced when desirable performance is provided, such as reduced heat to the affected region.
Based on the foregoing, it would be advantageous to provide a system that employs a wave pulse shaping mechanism that enables successful surgeries without delivering excessive heat to the surgical site, and allows operators to operate the phacoemulsification system effectively under both occluded and non-occluded conditions. It would also be beneficial to overcome the aforementioned drawbacks present in previously known ultrasonic tissue removal systems.